HTTP prefetching typically involves pre-requesting content on behalf of a client or browser before a request for that content is actually generated as a typical HTTP request and response in the course of a typical web page transaction. Certain prefetching embodiments involve pre-requesting content based on predictions about a future user selection without any actual action or selection by the user. Other HTTP prefetching systems, such as the systems discussed here, involve pre-requesting content in response to a user action or selection as part of a web page transaction. In such systems, when content is prefetched it may become possible to satisfy the request for that content locally (with regard to the client or browser) or at a location with a lower latency to the user, thereby negating the need to transmit the request and wait for the response from a content server. For example, in cases where there exists high latency between the client generating the request and the server which responds with the context requested, each negated request/response may avoid the penalty for such latency, thereby potentially reducing the total time required to satisfy the entire series of requests for the client. This may result in an accelerated end user experience.
In some prefetching systems, the system may have a set of metrics for determining when a file should or should not be prefetched. An ideal goal of a prefetcher may be to identify and prefetch all objects relating to a particular requested webpage, and to avoid prefetching objects which are not later requested by a user. For example, when a user requests a web page, the prefetcher may request (e.g., as a proxy for the user) various objects embedded in the webpage in anticipation of those objects being ultimately requested. Under certain circumstances, however, incorrect objects may be prefetched repeatedly based on incorrect models or difficult to quantify exceptions to a rule, resulting in resources being wasted to prefetch an object that will never be used. In certain cases, a prefetcher may miss objects that are embedded in a web page, and it may be difficult to determine which objects associated with a web page will ultimately be requested, or how an object seen at a proxy server relates to other objects. Such circumstances may result in slower performance and increased wait time for a user while a system fetches an object that was missed by a prefetcher.